Bulgarians had been subject to the Khazar Khanate until the collapse of this khanate (965) and they had paid taxed to the Khazar Khan. Pursuant to the collapse of this state, Bulgarians founded an independent khanate. The Kiev Princedom of Russia invaded the Bulgarian country in the years of 964 and 985. The invasion in 985 could not destroy the wealth of the Bulgarian country. Afterwards, the relation between the Bulgarians and Russians developed and they concluded a trade agreement in the year of 1006. However, the trade of firs in the north caused continuous wars between the Russians and Bulgarians since the second half of the century XI. These wars continued until the emergence of Mongols in the first half of the century XIII. Mongolians gained a victory after they defeated the Russians on the banks of Kalka River (1224). While they were returning to the east, they were busted by the Bulgarians and suffered lots of casualties. This event led to the collapse of the Idyll Bulgarian State. Batu Khan wanted to take revenge of this defeat. In the "West Expedition", the first target of the great Mongolian army under the command of Batu Khan was the Bulgarians. Mongolians attacked to Bulgarians in 1236 and they destroyed the villages and cities. Meanwhile, they despoiled the city of Bulgar with a population of fifty thousands of people. Pursuant to the Mongolian invasion, Bulgarians maintained their independency to a certain degree in the period of Golden Horde State (Golden Army) that was founded in Dest-i Kipchak. It has been observed that the city of Bulgar reinvigorated its old glorious state in a short period at the same time. Bulgarians sometimes opposed to the Golden Horde Khanate. As a result, the Golden Horde Khan, Pulat Timur punished the Bulgarians in the year of 1361 and the city of Bulgar was subjected to a new destruction. In the course of the military expedition carried out in 1391 by Timur against the Golden Horde Khan, Toktamis (1376-1395), the Bulgarian country was despoiled and destroyed again. The city of Bulgar was not much affected by the expedition of Timur upon Toktamis in 1395. As a result, Toktamis Khan who was defeated by Timur had to penetrate in the Bulgarian City together with some of his forces. We have observed that the city of Bulgar was destroyed by the Russians in 1399. However, the most probable reason for the collapse of this city was the development of Kazan City that was founded by Batu Khan. Bulgarians who could not regain their power again after 1399 got dispersed. Some of the people immigrated along the Kazan River in the north of Kama and settled in this region and they made the region to become a Turk region. The essential population of Kazan Khanate that was founded in the year of 1437 was composed of the Muslim people who were the hybrids of Bulgarians-Kipchak people.